In the first place, the printing from a color negative film will be explained below:
Generally speaking, an image plane of a color negative film has light and shade distribution, and the distribution of colors with blue, green and red densities differing according to various parts of the image plane, and said image plane is not necessarily considered to have been obtained by an appropriate exposure of the negative film, so that in the printing process, print exposures should be controlled according to the requirements for the negative film to be printed.
In most cases, however, color-balanced and print exposure-well-controlled color printing operations are practiced by controlling constant the transmission light quantities of the three-color components of blue, green and red in the entire area of an image. This is based on such an empirical rule that the three-color average reflectance obtained by integrating the entire scene is nearly constant in usual photographing scenes. Those skilled in the art call this "the gray integration printing method". Namely, when a normal, neutral subject is photographed on a color negative film, the large area transmittance density varies according to over- or under-exposure, the quality of a light source used in the photographing, the sensitivities of the blue-, green- and red-sensitive layers of the color negative film, the presence of a mask, and the like, and such variations are automatically controlled by keeping the exposures by blue, green and red lights constant at the time of the printing exposure operation.
In contrast to this, the change in the three colors of a color negative image caused due to the different distribution of the colors of a subject, since it leads to the change in the areal three-color component ratio of the subject, is of such a nature as not to be automatically controlled by such the conventionally practiced method as aforementioned.
And, the change in the densities of a negative film occurring in the case where a light-shade composition is extremely biased compared with normal light-shade distributions such as where the highlight area is extremely large or small as compared with normal scenes; for example, where a majority of the area of a scene is composed of shades or of highlights, is due to the areal change in the densities of a subject. In that case, therefore, the printing cannot be compensated by the conventional method that controls the printing merely according to the large area transmittance density. In addition, in the case where a principal subject is composed of extreme shadows or of extreme highlights as compared with other subjects surrounding the principal subject, the printing can not be compensated, either, because the set condition of the printer differs largely from the composition of such a scene.
Among the skilled in the art, the result obtained by photographing such a scene as to produce a color-unbalanced print is called the "color failure", while the result obtained by photographing such a scene as to produce an unsatisfactory density-having print is called the "density failure". Frequencies of the occurrence of such failures, although they vary according to seasons, are said to be around 5% for the color failure and from 30 to 40% for the density failure. For automatic correction of the color failure, the lowered correction method, etc., has been adopted and made a practical reality.
For automatic correction of the density failure, there have been proposed a method which is such that principal part of an image is finely divided into parts among which the highest density-having part is selected as one that represents the principal subject, and the functional relation between the highest density and the peripheral densities is used to determine a correcting quantity, and another method for determining a printing density by positionally weighting.
At the present time, in the printing by use of these probability procedures, the gray integration printing method produces 30 to 40% defective prints, and even the automatic negative judgement method wherein a negative image is finely devided into parts whose densities are used to determine a print exposure produces 5 to 10% defective prints. Besides, aside from such defects in print exposure, there are a few percent prints that are not allowed to be shipped because they are such faulty images as unexposed frame, blurred image, out- of-focus image, and the like.
Faulty image prints, if found before shipping and the shipping thereof is stopped, leads to only the loss of photographic papers. However, defective prints are usually reprinted and shipped. The reprinting operation process comprises finding defective prints, looking for the original negatives of the defective prints to conduct the reprinting thereof, and, after inserting the processed prints into the preceding group of prints. Even if there is only one defective print, the lot of prints to which the print belongs is not allowed to be shipped, so that the printing operation process becomes largely confused. Furthermore, the reprinting operation, because of the above-described procedures, require enormous time and labor as compared to the first printing operation process.
For this reason, measures are taken to prevent the occurrence of defective prints. A most generally conducted measure is such that a skilled operator is stationed at the printer (exposure section), and he checks one image after another of negative films to change print exposure for negative films that are likely to produce defective prints. For example, since an image having a principal subject (such as a portrait) as a highlight area surrounded with a dark area as in a strobe-scopic scene tends to produce a flat-toned print in the gray integration printing method for the reason described above, the operator perceives the dark area and the density of the principal subject to classify the negative image to thereby determine an appropriate print exposure according to his experience. And in the case of an image in which colors vary areally as in such a scene as of a red carpet, the gray integration printing method renders the entire area neutral-toned, so that the color of the red carpet cannot be reproduced as really red in a printed image. In that case, the operator changes the print exposure balance of red, green, and blue lights on the basis of his experience to thereby produce a print.
To enable such a printing control, an ordinary printer is provided with keys each having a geometrical exposure change range of from 20 to 10%, and the operator experiences which key should be selected from the keys in order to produce a satisfactory print, and on the basis of the experience, the operator makes key selections in the routine printing process. As the operator becomes most skillful in the operation of the printer, he becomes able to reduce the rate of making defective prints to a few percent. As means to effectively employ these skilled operators, the judgement of negative film image qualities is provided independently of the printer, and according to the results of the judgement, unmanned automatic operations of the printer may be carried out--this has been made a practical reality. Further, in order to minimize the loss of prints likely to be produced as a result of the determination of print exposures by use of the earlier-mentioned scanned densities, a measure is taken to have the operator judge negative image qualities in advance in the stage prior to the printer operation. These measures require skilled operators on condition that the image quality judgement is made artificially on one frame by one frame with the estimation by the operator of automatically controlled results in the printer.
On the other hand, exposure-determining devices which employ a video system are practically used. A typical example of such devices is a device having a flying spot scanner as a light source which scans the entire area of a negative film image to photoelectrically detect the change in the quantity of light corresponding to the densities of the negative image, and the photoelectric signals are reversed to thereby reproduce a positive image on a CRT screen. The observer, viewing the positive image on the CRT screen, if the image is darker on the whole, changes and controls the quantity of the light of the flying spot scanner so as to reproduce a visually satisfactory image. The value obtained by the control of the quantity of the light is used as the quantity of light for use in the printing process. The same principle may be applied to both color and black and white printing processes. This has been used in the determination of print exposures for making professional prints (large format prints), but the acceptable ranges of the independent judgement of each frame image and of the color adjustment and luminance adjustment of the CRT screen image, because the human eye becomes adapting to the CRT screen image, becomes so wider that the operator needs to become more skillful to be able to cause the adjusted level to correspond with the print exposure. And the judgement of image qualities one frame by one frame requires enormous time, so that it is not adopted in the process of making prints for general users.